Cleaning of metallic surfaces



. fcaptothiazolines'.

Patented Mar. 6,, 195.1

CLEANING F METALLIC SURFACES Richard 0. Zerbe, Nitro, W. Va., assignor to Monsanto Chemical Company, St. Louis, Mo., a cor- Duration of Delaware i" No Drawing. Application February 9, 1948,

Serial No. 7,297

18 Claims. 1

invention relates to the cleaning of metalllic surfaces and particularly to processes and {compositions which employ steel pickling inhibitcirs herein describedin conjunction with an "ac d.

Pickling solutions for. removing oxides from the surfaces of metals ordinarily consist largely of a dilute solution of an inorganic acid such as sulfuric or hydrochloric acid. The acid although it dissolves theoxides and scale, also attacks the metal to some extent so that the acid is largely consumed and a certain amount of metal is lost. It also appears that the hydrogen libernoted by the action of the acid on the'metal has za serious embrittling effect upon the metal being treated. The escaping hydrogen also carries with it a fine spray of the acid liquor from the pickling bath which produces an atomsphere possessing corrosive properties and one which injurious to health and damagingv to equipment.

By the present invention, these objectionable :features of the pickling process are substantially overcome or reduced to a minimum. More specifically, some of the objects of the present inyention are to obviate over-pickling, embrittle- :-ment and pitting of the articles treated; to min- :imize the amount of metal lost in pickling; to increase the eificincy of the pickling operation;

to prolong the effective life of the pickling bath;

and particularly to facilitate the pickling operation. Other and further objects of the invention will be apparent from the following description and accompanying examples.

To accomplish to as great an extent as possible the objects set forth in accordance with the present invention, there is added to the pickling bath an inhibitor or regulating agent which acts to restrain the action of the acid from attacking clean metal but assists in remov- "ing the rust, scale, and other deposits or in other tvords the inhibitor causes the acid selectively "fjto remove such materials without appreciably j attacking the clean portions of the metal under treatment.

The new class of pickle regulators may be classed as hydroxy polyether derivatives of mer; Hydroxy ethyl mercaptothi-g azoline is known to be a pickling inhibitor but; it is not soluble in the pickling baths and special techniques have been attempted in order to disperse the material in the acid cleaning solutions. However, it has now been found in accordance with the present invention that the hydroxy polyether derivatives of mercaptothiazolines are highly effective pickle regulators which are at the same time soluble in the pickling baths. The new inhibitors contain atle'ast two ether linkages and one or more hydroxyl groups. Thus, the new class of pickling inhibitors may be represented by the general formula our-N where R1 and R2 are alkylene groups and n is an integer.

The new inhibitors may be prepared by condensing a mercaptothiazoline with ethylene oxide, propylene oxide, epichlorhydrin, glycerol 0. chlor hydrin, glycide, glycol, glycerol, polyglycerol, and the like. Two or more of these reactive compounds may also be caused to react consecutively. The condensation is advantangeously carried out in the presence of alkaline reacting agents or nickel sulfate as catalysts.

Examples of mercaptothiazolines which will condense with the above mentioned reactive compounds to give excellent pickling inhibitors are 2-mercaptothiazoline and substituted 2-mercaptothlazolines wherein one or more of the hydrogen atoms attached to the carbon atoms in the 4 and 5 positions of the thiazoline nucleus are replaced by saturated-and unsaturated hydrocarbon groups such as alkyl, alkylene, aryl,

" aralykyl, or cycloaliphatic groups.

The ready solubility of the new inhibitors in the pickling baths is an important quality. The problem of dispersing insoluble inhibitors is a troublesome one and the presence of undissolved particles in the cleaning bath frequently results in spotting and staining of the metal pieces. Solubility determinations carried out in cold dilute acid with condensation products of 2-mercaptothiazoline and ethylene oxide and of 2 mercaptothiazoline and propylene oxide revealed that the solubility increased with increasing values of n in the foregoing formula. Mercap tothiazoline-ethylene oxide condensation prod-- nets in which the value of n was greater than l were completely soluble in'hot pickling baths in the amounts normally used and produced clear haze free pickling baths. In general the preferred value of n is within the range of 230. It is usually preferred to employbetween about one hundredth of one percent and three hundredths of one percent by weight based on the pickling bath. However, the composition, concentration, temperature of operation, and other factors vary with diiferent baths and similarly the optimum concentration of inhibitor will vary f l l me a .ieular. conditions ernp oyed. Theconcentration of inhibitor based on the quantity of 100 percent acid con.- tained in the pickling bath is usually between about two tenths of one per c ent andihgglf. gf one percent.

As exemplary of the preparatigrr gigtlge newi hibitors Z-mercaptothiazoline was condensed with ethylene oxide in varying ratios. 23.8 parts by weight (substantially 0.2 mol) .of zemercapto'thiarzoline and 0.25 parts by weight of powdered--potassium hydroxide were charged into tale-Suitable reaction vessel. The mixture was melted by im w. a 1 an 9 b t lead th eth e ox ei tte i i i eizne l thraue'h n lundu lae l' iC- .fs l les .we eie en a i t .a dt sfid e ihe' I bit ne elueilntnis II-K15 .wermprenared where R. is an ethylene group and n is an integer. While n is a whole number in the case of any given molecule, it -is. convenient to designate n as a function of the average molecular weight a m re fi qul th t ta molecu a we ght eqfiivaients "of" ethylene oxide actually reacted w th Ke t aqlee le we ht .Q m a e cl c ema: va e n n e le acted per irnolbf rnercaptothiazoline and thereassumes fra'ctionalyalues.

jn fi ee l'fe ii il ei ent w i h b 1 M 1 ati of e ente a d e PWWPFY? eer i ty ica mp enref rreq e 9?; mate als w re, e p oyed in thein'etal pickling process under conditions 33 1 1. 5 e as ee al t se e 9;, compounds and itsyal e anprax zn tely 6%. y .t i- 66.Be;,s 1f;uric anqas al amqun (i o e of. theinhibitors ll ie ta qss aS m analogous manner but without theuse, of any. in.- hi tor .18 th mb f Q m le ethy ene o de ..,mini. aame eete9i;iheinmtitinay iueofthe'compound employed. The results obtained t al loss compared withtest piecetreated man...

on testing'typical examples of the preferred class of materials are given in the following table. The metal lossis reported as the average of duplicate determination.

Table oer-N CS'-C1H40(C H O),.H

CHr-S 'IZotal 156s of 1 l amount; metal. in Remarks Grains Grams 'Blank no inhibitor 0. 7764 strips pitted.

LL 2.030936. Inhibitor not soluble. White wax remained in bath. \;..0.95 "0.0936 0 0145 Inhibitor not completely soluble. 7v 1 Oily droplets remaincd in bath. 212.8; $.(l'ail936 0. 0098 Inhibitor completely soluble. Picki E led strips clean and bright. 8 2 0(23'40 0'. 00 88 D0. 7

5 O. 095 0. 0093 D0. Z755 [F2340 (P0075 DO.

.;.It-.-is:;apparent from the data set forth that introducing more than one ether group into the molecule enhanced. solubility in the:pick1ing;bath and .that compounds containing appro irnately three ether.- linkages are not only completely solu .ble butpossesshigher inhibiting efficiency. Conrparing thelQss'in. weight-fofthesteel test s ips .toitheJoss :whennoinhibitor was employed, at is .obvio.us 'Lthat-a g'grfeat saving in m'etal effected eofthe.newirihibitorS. H v V ther methods of .er nployin'g ihhibitbrsfof Ethe .clajss hereinbefore set forth in acid pickling camera-15am apparent 'to thofsesk-illed in the art .to which "the \invention. :pertaina The -products described may be employed in the --presenc e of foaming agents, iionizable -su b'st'ances o'r ;othe r materials ordinarily used. Thus the preferred class .of materials m'aylbeen ployed asthe sole in hfloitor .orfthey may be employed in conjunction with .olthenmaterials exhibiting an inhibiting'action .or with. inert fillers, dispersing agents. etc. Other non-oxidizing mineral acids' than sulfuric acid may be used "in the pickling bath in conjunction with the preferred class of inhib tors in the manner hereinbefore set forth.

What is claimed is: p I U x 1'. .A process of. pickling a metal consisting essentially of. subjecting the metal to'be pickled tofthe action of a heatednon-o idizingmineral acid. solution containing a small-amount Slim-' cient to. inhibitthe. action ofthe acid on the metal of; a .compoundof the structure one-err i'ws' ereRriand R21 are aikylene grouesand n w th integer: gre'ater than one.

"21A: process of pickling. metal consisting" one but. not more than 30.

3Z'A' prOGsS' dfpi'clilirig 'a metal" deflectingvhere R1 and R2 are alkylene groups o'i less tham carbon atoms and n is approximately three:

4. A process of pickling a metal consisting? :ssentially of subjecting the metal to berpickiedi so the action of a heatednon oxidizing'minerall acid solution containing a small amour-it'- suit-- cient to inhibit the action of the acid on the metal 7 of a compound of the structure CHz-N l c-sR1o-- R,oa ,.B

where R1 and R2 are ethylene groups and n is an integer greater than one but not more than 30.

5. A process of pickling a metal consisting essentially of subjecting the metal to be pickled to the action of a heated non oxidizing mineral acid solution containing a small amotmti sum.- cient to inhibit the action of the acid on the metal. of a compound of the structure where R1 and R2 are propylene groups and n is an.

integer greater than one but not more than 30.

6. A process of pickling a metal consisting essentially of subjecting the metal to be pickled to the action of a heated sulfuric acid solution containing a small amount sufficient to inhibit the action of the acid on the metal of a compound of the structure where R is an ethylene group and n is an integer greater than one but not more than 30.

'7. A process of pickling a metal consisting where R is an ethylene group and n is approximately three.

8. A process of pickling a metal consisting essentially of subjecting the metal to be pickled to the action of a heated sulfuric acid solution containing a small amount sufiicient to inhibit the action of the acid on the metal of a compound of the structure where R is an ethylene group and n is approximately eight.

9. A pickling bath for metal products consisting essentially of a non oxidizing mineral acid solution containing a small amount sufficient to inhibit the action of the acid on the rhetal ofiafi compound of the structure where R1 and R2 are alkylene groups and n is aninteger greater than one.

10. A pickling bath for metal products eonsist ing essentially of a non oxidizing miiieral acid' solution containing 0.01 to 0.03 percent'liy weight based on the pickling bath of a COIIIPOllliCIZOfIhG-i structure oHr-N where R1 and R2 are alkylene groups of less than 4 carbon atoms and n is an integer greater than one but not more than 30.

11. A pickling bath for metal products consisting essentially of a non oxidizing mineral acid solution containing 0.01 to 0.03 percent by weight based on the pickling bath of a compound of the structure OHS-N c-s-R,o-(R,0)..H

cHz-s where R1 and R2 are alkylene groups of less than 4 carbon atoms and n is approximately three. 12. A pickling bath for metal products consisting essentially of a non oxidizing mineral acid solution containing 0.01 to 0.03 percent by weight based on the pickling bath of a compound. of the structure CH N c-sR1o(R,o)..H

CH -S where R1 and R2 are ethylene groups and n is art integer greater than one but not more than 30. 13. A pickling bath for metal products consisting essentially of a non oxidizing mineral acid solution containing 0.01 to 0.03 percent by weight based on the pickling bath of a compound of the Structure CH -N C-SR10-(RzO)nH CHS where R1 and R2 are propylene groups and n is an: integer greater than one but not more than 30. 14. A pickling bath for metal products consisting essentially of a sulfuric acid solution containing 0.01 to 0.03 percent by weight based on the pickling bath of a compound of the structure GET-N o-sRo- Ro),.H

CHr-S where R is an ethylene group and n is an integer greater than one but not more than 30.

15. A pickling bath for metal products consisting essentially of a sulfuric acid solution containmg 0.01 to 0.03 percent by weight based on the pickling bath of a compound of the structure CH -N c-s-nonomi GHQ-S where R is an ethylene group and n is approximately three. 

10. A PICKLING BATH FOR METAL PRODUCTS CONSISTING ESSENTIALLY OF A NON OXIDIZING MINERAL ACID SOLUTION CONTAINING 0.01 TO 0.03 PERCENT BY WEIGHT BASED ON THE PICKLING BATH OF A COMPOUND OF THE STRUCTURE 